This invention relates to a foamed or expanded body of low bulk density composed principally of ceramic fibers and a method of making same.
The term "ceramic fibers" as used herein means polycrystalline metal oxide fibers having a high melt temperature typically in excess of 3,000.degree. F. Ceramic fibers generally contain aluminum oxide or calcium oxide and silica, as well as smaller amounts of other metal oxides, such as ferric, titanium and magnesium. A typical ceramic fiber will comprise, for example, in excess of 30% aluminum or calcium oxide, in excess of 45% silica, with any remainder as other metallic oxides. As used herein, therefore, the term "ceramic fibers" excludes other inorganic fibers such as asbestos and glass fibers.
Ceramic fibers are manufactured by several known processes, one of which involves the formation of a slag melt at a temperature in excess of 3200.degree. F., and then contacting a spinning or slinging wheel or high velocity gas with the melt to produce individual fibers having a fixed range of diameters, which are then cooled and collected. Various compositions for ceramic fibers and methods for making the same are described in the following U.S. Pat. Nos.: 2,557,834; 2,674,539; 2,699,397; 2,710,261; 2,714,622; and 3,007,806.
Ceramic fibers have a variety of present uses, and are used primarily in bulk form as fillers and insulating media. One problem with ceramic fibers is that they are not easily wetted with liquids and tend to clot, rather than disperse, in water, even with the addition of dispersion processing aids.
In contrast, asbestos, a naturally occuring mineral, is made up of bundles of fibers that can be mechanically or chemically opened up and reduced to small diameter fibers that are easily dispersed in water. Examples of asbestos dispersions are described in the following U.S. Pat. Nos.: 2,972,221; 3,630,012; 3,738,805; 2,626,213; 3,676,038; 3,338,994; and 3,806,572.
Because asbestos fibers quickly and easily form a stable aqueous dispersion, it is possible to whip the dispersion and prepare a stable foam body, as described in U.S. Pat. No. 3,338,994 and U.S. Pat. No. 3,461,191. These patents disclose preparing a dispersion of asbestos in water containing a surfactant. Unfortunately, however, these processes are not applicable to ceramic fibers and do not result in a stable dispersion or suspension that is adaptable to making foam products.
It would be desirable to prepare an elastic, light weight material from ceramic fibers for several reasons. First, ceramic fibers have greater temperature resistance than other inorganic fibers such as asbestos and glass. Second, to the extent that asbestos may constitute a potential health problem, it would be desirable to provide a heat resistant foam that is free from asbestos.